Semiconductor integrated circuit device and testing method therefor

ABSTRACT

A gunning transceiver logic input circuit is provided a construction, in which a high potential power source for a differential input circuit and a high potential power source for an internal CMOS circuit are mutually separated and independent of each other, upon performing an IDDQ test as a static current measuring test for an LSI including the differential input circuit flowing a steady-state current and an internal CMOS circuit not flowing the steady-state current. Upon IDDQ test, IDDQ test becomes possible to perform power supply from the power source independent from the power source of other CMOS circuit.

This is a divisional of application Ser. No. 09/120,100 (ConfirmationNumber not yet assigned) filed Jul. 22, 1998, now U.S. Pat. No.6,249,134 the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a semiconductor integratedcircuit device and a testing method therefor. More particularly, theinvention relates to a semiconductor integrated circuit device loaded adifferential circuit and a CMOS (Complementary Metal-OxideSemiconductor) circuit and an IDDQ (Quiescent IDD) testing circuittherefor.

2. Description of the Related Art

In a CMOS LSI as a primary semiconductor integrated circuit, demands forhigher density and higher speed have been growing. Particularly, asystem frequency required for LSI has currently reached in an order ofseveral hundreds MHz. An important task for satisfying such demand ishow to improve operation frequency of an LSI output.

As one method for achieving the task, high speed circuits, such as GTL(Gunning Transceiver Logic) circuit, have been proposed. As to the GTLcircuit, reference is made to “A CMOS Low-Voltage-SwingTransmission-Line Transceiver” in “ISSCC 92/SESSION 3/HIGH PERFORMANCECIRCUITS/PAPER WP 3.7 (pp. 58 to 59) reported in IEEE INTERNATIONALSOLID-STATE CIRCUIT CONFERENCE, 1992 and “Solid State ProductsEngineering Council”, JEDEC, 1991 and so forth. Most of these circuitsachieve high frequency output by making output amplitude smaller.Accordingly, a counterpart LSI input interfacing the LSI output has tobe an input circuit corresponding to small amplitude.

FIG. 3 is an illustration showing a construction of an LSI loaded a GTLoutput circuit a. On an LSI 20, a GTL input circuit b is loaded. On theother hand, in a connection wire 30 connecting a GTL output circuit aand the GTL input circuit b, a terminal resistor R having relatively lowresistance value is provided. Through the terminal resistor R, aterminal voltage VT is applied to the connection wire 30.

FIG. 4 is an illustration showing an example of the GTL input circuit b.The GTL input circuit b has a differential circuit constructionconsisted of P-type MOS transistors T1 and T2. Namely, on a gate of thetransistor T1, an input Vin is supplied, and on a gate of the transistorT2, a reference voltage Vref is supplied, respectively. Between a commonsource of both transistors T1 and T2 and a high potential power sourceVDD, a P-type MOS transistor T3 is provided. To the gate of thetransistor T3, the input Vin is supplied.

As drain loads of both transistors T1 and T2, a current mirror circuitconsisted of N-type MOS transistors T4 and T5 is provided. An outputVout is lead from a drain of the transistor T2 via an inverter(generally a CMOS inverter) 1.

In the circuit constructed as set forth above, high frequency operationcan be realized easily in comparison with a normal CMOS input circuit.The reason is as follows. A logic signal in the normal CMOS circuitcorresponds to VDD (high potential power source voltage of the circuit)at high level, and to a ground level at low level. In contrast to this,the differential input circuit of FIG. 4 is operative at a high levelcorresponding to a voltage between VDD and Vref, and a low levelcorresponding to a voltage between Vref and the ground potential toassure stable operation even with a low amplitude input signal.

FIG. 5 shows one example of a relationship of voltage levels atrespective parts in the construction of FIG. 3. In the shown example itis assumed that power source voltage VDD=5V, the terminal voltageVT=1.2V and the reference voltage Vref=0.8V. On the other hand, the GTLoutput circuit is operative between a high level normally being VT and alow level (Vol) normally in a range of 0<Vol<0.4V. In the circuitconstruction shown in FIG. 4, a drain output of the transistor T2applied the reference voltage Vref at the gate thereof is converted intoa normal CMOS level by the inverter 1, and thereafter the signal ispropagated within the LSI 20.

In the circuit of CMOS structure, while a through current flows uponvariation of the signal, little current may flow in steady state.However, when a faulty portion is present in an internal circuit of theLSI and a short circuit is formed between the power source or the groundby such faulty portion, a current flows even in the steady state.Accordingly, testing whether failure is caused in an element of theinternal circuit of the LSI or not, can be performed by measuring aconsumed current in the steady state. This will be referred to as IDDQtest (static current consumption measuring test: Quiescent IDD test),which is new testing method recently introduced for improving failuredetection ratio supplementing a function test employing a test pattern.

On the other hand, a differential circuit shown in FIG. 4 is normallyconstructed to flow a steady-state current. Therefore, in the steadystate (static state) of the LSI, the current may flow in spite of thefact that the LSI operates normally. Therefore, a differential circuithaving a circuit construction as shown in FIG. 6 can be considered.Namely, an enabling signal Ven is supplied to the gate of the P-typetransistor T3 in the circuit of FIG. 4, and, by providing N-typetransistor T6 between the drain of the transistor T2 and the ground, theenabling signal Ven is supplied to the gate of the transistor T6.

In the construction set forth above, by setting the enabling signal Venat high level, the steady-state current can be cut. However, at thistime, the output Vout is fixed at high level irrespective of the valueof the input Vin. In a current cut state, IDDQ test can not beimplemented by an optimal IDDQ test pattern.

In the conventional CMOS LSI loaded the differential circuit, it has notbeen possible to perform effective IDDQ test.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide asemiconductor integrated circuit device loaded a differential circuitflowing a current in a steady state, which can be implemented anappropriate IDDQ test.

It is another object of the present invention to provide a testingmethod for a CMOS LSI loaded a differential circuit flowing a current ina steady state, which can implement an appropriate IDDQ test.

According to the first aspect of the present invention, a semiconductorintegrated circuit device including a differential circuit flowing asteady-state current and an internal circuit not flowing thesteady-state current, comprises:

a high potential power source for the internal circuit; and

a high potential power source for the differential circuit separatelyand independently.

In the preferred construction, a terminal for the high potential powersource of the differential circuit and a terminal for the high potentialpower source of the internal circuit may be provided independently ofeach other. The differential circuit may be an input circuit inputtingan output signal of other integrated circuit to the internal circuit asan input.

Preferably, the differential circuit is a gunning transceiver logiccircuit. Also, the internal circuit may be a circuit of a CMOSstructure. More preferably, the circuit of the CMOS structure is a CMOSinverter.

According to the second aspect of the present invention, a testingmethod for a semiconductor integrated circuit including a differentialcircuit flowing a steady-state current, a first terminal of the highpotential power source of the differential circuit, and a secondterminal for the high potential power source of the internal circuit,comprises:

first step supplying power source voltages to the first terminal and thesecond terminal from mutually independent power sources;

second step of performing a consumed current measuring test in the powersource of the second terminal in a condition where power source voltagesto the first terminal and the second terminal are supplied from mutuallyindependent power sources.

The measuring test of the second step is preferably a measuring test ofa static consumed current. In the preferred embodiment, after completingthe measurement test of the second step, the first ands second terminalsare connected in common.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiment of the present invention, which, however, shouldnot be taken to be limitative to the invention, but are for explanationand understanding only.

In the drawings:

FIG. 1 is a circuit diagram showing the preferred embodiment of asemiconductor integrated circuit device according to the presentinvention;

FIG. 2 is a flowchart showing the preferred embodiment of a testingmethod of the semiconductor integrated circuit device according to thepresent invention;

FIG. 3 is an illustration showing a construction of an LSI loaded a GTLcircuit;

FIG. 4 is an illustration showing a construction of a differentialcircuit as the GTL circuit;

FIG. 5 is an illustration showing a signal waveform of the LSI and arelationship of voltages at respective portions; and

FIG. 6 is an illustration showing the example of construction of thedifferential circuit of the conventional GTL circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be discussed hereinafter in detail in termsof the preferred embodiment of the present invention with reference tothe accompanying drawings. In the following description, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be obvious, however, tothose skilled in the art that the present invention may be practicedwithout these specific details. In other instance, well-known structuresare not shown in detail in order to avoid unnecessarily obscure thepresent invention.

FIG. 1 shows the preferred embodiment of a semiconductor integratedcircuit device according to the present invention. In the followingdisclosure, like reference numerals identify like elements in FIG. 4 anddetailed description for the common elements will be neglected in orderto keep the disclosure simple enough by avoiding redundant discussionfor facilitating the clear understanding of the present invention.Therefore, the following discussion will be concentrated to the portiondifferent from that in FIG. 4. A high potential power source VDD1 of adifferential input circuit as a GTL input circuit consisted oftransistors T1 to T5 is provided separately and independently of a highpotential power source VDD of an internal circuit (including an inverter1) of another CMOS structure. Namely, external terminals for supplyingpower sources VDD1 and VDD are provided mutually independently.

An inverter 1 connected to an output portion of the differential inputcircuit is an inverter circuit of general CMOS structure which isconsisted of a P-type MOS transistor T7 and an NMOS transistor T8. Alevel of the output Vout is converted into a CMOS level by the inverter1.

In an IDDQ test, as shown in a flowchart of FIG. 2, as an operationalpower source VDD1 of the differential input circuit flowing a current ina steady state, a power source different from operational power sourceVDD of other internal circuit, is supplied independently (step Si), andmeasurement of the IDDQ is performed (step S2). In this case, theoperational power source VDD is supplied only to an internal CMOScircuit, through which a current does not flow in the steady state, aresult of measurement of the IDDQ representing a consumed current of thepower source VDD becomes a current value “0”. On the other hand, whenthe abnormal circuit is present even one, the result of measurement ofthe IDDQ will not become “0”. Therefore, detection of abnormality in afabrication process becomes possible.

At this time, a ratio of number of elements in the differential inputcircuit in number of elements in the overall LSI becomes quite small.Therefore, effect can be sufficiently guaranteed only by performing IDDQtest for the power source VDD.

The power sources VDD and VDD1 are separated and independent. Only, inthe a testing stage of the wafer in the factory, VDD and VDD1 aresupplied independently from the power sources. When the LSI is mountedon a circuit board, these power sources are connected in common (stepS3). Therefore, when a user uses the LSI, both power sources VDD1 andVDD can be regarded as the same power source.

In the embodiment of FIG. 1, to the gate of the transistor T2 of thedifferential circuit, a reference voltage Vref is supplied. Thereference voltage Vref is derived as

 (High level+Low level of Vin))/2

and is supplied externally. Because of the differential circuit, it isalso possible to supply an inverted signal of Vin.

As set forth above, according to the present invention, in the CMOS LSIloaded the GTL input circuit flowing the current even in the steadystate, improvement of a LSI failure detection ratio by the IDDQ test canbe achieved similarly to the prior art. By this, it becomes possible toavoid shipping of faulty product in the fabrication process. The reasonis that the high potential power source of the differential circuit isseparately and independently of that of other internal circuit to permitimplementation of the IDDQ test in the same manner as that of theconventional IDDQ test standard.

Although the present invention has been illustrated and described withrespect to exemplary embodiment thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be understood as limited to thespecific embodiment set out above but to include all possibleembodiments which can be embodied within a scope encompassed andequivalents thereof with respect to the feature set out in the appendedclaims.

What is claimed is:
 1. A semiconductor integrated circuit devicecomprising: a differential circuit configured to have a steady-statecurrent flow; an internal circuit not having the steady-state currentflowing therethrough, said internal circuit being connected to an outputof said differential circuit; a first terminal for receiving input froma first high potential power source as an input for said internalcircuit; and a second terminal for receiving input from a second highpotential power source as an input for said differential circuit,wherein said first terminal and said second terminal are providedindependently of each other.
 2. A semiconductor integrated circuitdevice as set forth in claim 1, wherein said differential circuit is aninput circuit inputting an output signal of other integrated circuit tosaid internal circuit as input.
 3. A semiconductor integrated circuitdevice as set forth in claim 2, wherein said differential circuit is agunning transceiver logic circuit.
 4. A semiconductor integrated circuitdevice as set forth in claim 3, wherein said internal circuit is acircuit of a CMOS structure.
 5. A semiconductor integrated circuitdevice as set forth in claim 4, wherein said circuit of the CMOSstructure is a CMOS inverter.